• Research indicates that brain peptides exert both behavioral and endocrinologic effects in humans and animals. This review summarizes the best known behavioral actions of four endogenous peptides: luteinizing hormone-releasing hormone (LHRH), adrenocorticotrophic hormone (ACTH), vasopressin, and angiotensin. The hypothalamic-releasing hormones play a role in modulating pituitary-end organ systems. Behavioral disorders may, in the future, be susceptible to formulation in terms of changes in brain peptides. Peptide research in psychiatry may be approached in several ways.